Body contacted hybrid surface semiconductor-on-insulator devices

ABSTRACT

A portion of a top semiconductor layer of a semiconductor-on-insulator (SOI) substrate is patterned into a semiconductor fin having substantially vertical sidewalls. A portion of a body region of the semiconductor fin is exposed on a top surface of the semiconductor fin between two source regions having a doping of a conductivity type opposite to the body region of the semiconductor fin. A metal semiconductor alloy portion is formed directly on the two source regions and the top surface of the exposed body region between the two source regions. The doping concentration of the exposed top portion of the body region may be increased by ion implantation to provide a low-resistance contact to the body region, or a recombination region having a high-density of crystalline defects may be formed. A hybrid surface semiconductor-on-insulator (HSSOI) metal-oxide-semiconductor-field-effect-transistor (MOSFET) thus formed has a body region that is electrically tied to the source region.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/454,518 filed on Apr. 24, 2012, which is a divisional of U.S. patentapplication Ser. No. 12/342,373, filed Dec. 23, 2008 the entire contentand disclosure of which is incorporated herein by reference.

BACKGROUND

The present invention relates to semiconductor devices, andparticularly, to body contacted hybrid surfacesemiconductor-on-insulator (HSSOI) devices formed on asemiconductor-on-insulator (SOI) substrate and methods of manufacturingthe same.

Hybrid surface semiconductor-on-insulator (HSSOI) devices refer tosemiconductor devices formed employing a sidewall of a top semiconductorlayer of a semiconductor-on-insulator (SOI) substrate. HSSOI devices maybe formed on the same SOI substrate as a planar semiconductor deviceemploying a semiconductor surface that is parallel to a top surface ofthe top semiconductor layer.

Electrical characteristics of the HSSOI devices display features oftypical SOI devices. Particularly, the floating body effect may place alimitation on performance parameters of HSSOI devices. An importantfactor in optimizing the power and performance advantages of HSSOIdevices is precise control of the voltage of the floating body.

BRIEF SUMMARY

An embodiment of the present invention provides a hybrid surfacesemiconductor-on-insulator (HSSOI) metal-oxide-semiconductor fieldeffect transistor (MOSFET) having a body electrically tied to a source,thereby minimizing or eliminating the floating body effect of the HSSOIMOSFET.

According to an aspect of the present invention, a portion of a topsemiconductor layer of a semiconductor-on-insulator (SOI) substrate ispatterned into a semiconductor fin having substantially verticalsidewalls. A portion of a body region of the semiconductor fin isexposed on a top surface of the semiconductor fin between two sourceregions having a doping of a conductivity type opposite to the bodyregion of the semiconductor fin. A metal semiconductor alloy portion isformed directly on the two source regions and the top surface of theexposed body region between the two source regions. The dopingconcentration of the exposed top portion of the body region may beincreased by ion implantation to provide a low resistance contact to thebody region. A hybrid surface semiconductor-on-insulator (HSSOI)metal-oxide-semiconductor field effect transistor (MOSFET) thus formedhas a body region that is electrically tied to the source region.

According to another aspect of the present invention, a semiconductorstructure is provided, which comprises: a semiconductor fin having afirst sidewall, a second sidewall, and a substantially horizontal topsurface and located directly on an insulator layer, wherein the firstand second sidewalls are substantially parallel to each other andsubstantially vertical; a body region located within the semiconductorfin and having a doping of a first conductivity type and verticallyabutting the insulator layer; a first source region located within afirst end of the semiconductor fin and directly on the first sidewalland having a doping of a second conductivity type, wherein the secondconductivity type is the opposite of the first conductivity type; asecond source region located within the first end of the semiconductorfin and directly on the second sidewall and having a doping of thesecond conductivity type; and a metal semiconductor alloy portionabutting the first source region, the second source region, and a topsurface of a portion of the semiconductor fin having a doping of thefirst conductivity type and located between the first source region andthe second source region.

The semiconductor structure may be a metal-oxide-semiconductor fieldeffect transistor (MOSFET) having a first channel directly beneath thefirst sidewall and a second channel directly beneath the secondsidewall, wherein current flows in a horizontal direction along thefirst sidewall and the second sidewall in the first channel and thesecond channel, respectively.

According to another aspect of the present invention, a method offorming a semiconductor structure is provided, which comprises: forminga semiconductor fin having a first sidewall, a second sidewall, and asubstantially horizontal top surface and located directly on aninsulator layer and having a doping of a first conductivity type,wherein the first and second sidewalls are substantially parallel toeach other and substantially vertical; forming a first source regionhaving a doping of a second conductivity type directly on the firstsidewall within a first end of the semiconductor fin, wherein the secondconductivity type is the opposite of the first conductivity type;forming a second source region having a doping of the secondconductivity type directly on the second sidewall within the first endof the semiconductor fin; and forming a metal semiconductor alloyportion directly on the first source region, the second source region,and a top surface of a portion of the semiconductor fin having a dopingof the first conductivity type and located between the first sourceregion and the second source region.

An embodiment of the present invention provides a hybrid surfacesemiconductor-on-insulator (HSSOI) metal-oxide-semiconductor fieldeffect transistor (MOSFET) having a body with selective leakage to asource, thereby optimizing the floating body effect of the HSSOI MOSFET.

According to an aspect of the present invention, a portion of a topsemiconductor layer of a semiconductor-on-insulator (SOI) substrate ispatterned into a semiconductor fin having substantially verticalsidewalls. A portion of a body region of the semiconductor fin isexposed on a top surface of the semiconductor fin between two sourceregions having a doping of a conductivity type opposite to the bodyregion of the semiconductor fin. A generation/recombination region isformed by at least one of several means. In one embodiment a regionhaving a high density of crystalline defects is formed by amorphizingthe exposed body region. A metal semiconductor alloy portion is formeddirectly on the two source regions and the recombination region betweenthe two source regions. The recombination region facilitates removal ofelectrical charges in the body region by increasing the recombinationrate of electrons and holes, thereby reducing or eliminating floatingbody effect. Alternatively, a metal-semiconductor interface over theexposed body region provides generation/recombination centers. A hybridsurface semiconductor-on-insulator (HSSOI) metal-oxide-semiconductorfield effect transistor (MOSFET) thus formed has a body region thatpreferentially has increased electrical leakage to the source. Thisallows increased body doping while maintaining low forward voltage onthe body with respect to the source.

According to another aspect of the present invention, a semiconductorstructure is provided, which comprises: a semiconductor fin having afirst sidewall, a second sidewall, and a substantially horizontal topsurface and located directly on an insulator layer of a substrate,wherein the first and second sidewalls are substantially parallel toeach other and substantially vertical; a body region located within thesemiconductor fin and having a doping of a first conductivity type andvertically abutting the insulator layer; arecombination-center-containing semiconductor region located directlyunderneath the substantially horizontal top surface and including anamorphized semiconductor material having a doping of the firstconductivity type; and a metal semiconductor alloy portion abutting therecombination-center-containing semiconductor region and at least onesource region that is located within the semiconductor fin and having adoping of a second conductivity type, wherein the second conductivitytype is the opposite of the first conductivity type.

The semiconductor structure may further comprise another metalsemiconductor alloy portion abutting the drain region at the firstsidewall, the second sidewall, and the end wall.

The first source region may not abut the second source region and may beseparated from the second source region by the body region. Alternately,the first source region and the second source region may be of integraland unitary construction.

According to another aspect of the present invention, a method offorming a semiconductor structure is provided, which comprises: forminga semiconductor fin having a first sidewall, a second sidewall, and asubstantially horizontal top surface and located directly on aninsulator layer and having a doping of a first conductivity type,wherein the first and second sidewalls are substantially parallel toeach other and substantially vertical; forming arecombination-center-containing semiconductor region directly underneaththe substantially horizontal top surface and including an amorphizedsemiconductor material and having a doping of the first conductivitytype; and forming a metal semiconductor alloy portion directly on therecombination-center-containing semiconductor region and at least onesource region formed within the semiconductor fin and having a doping ofa second conductivity type, wherein the second conductivity type is theopposite of the first conductivity type.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For all of the figures herein, the following conventions apply. Figureswith the same numeric label correspond to the same stage ofmanufacturing in the same embodiment. Figures with the suffix “A” aretop-down views. Figures with the suffix “B” are horizontalcross-sectional views along the plane B-B′. Figures with the suffix “C,”“D,” “E,” or “F” are vertical cross-sectional views along the planeC-C′, D-D′, E-E′, or F-F′, respectively, of the corresponding figurewith the same numeric label and the suffix “A.”

FIGS. 1A-7F are sequential views of a first exemplary hybrid surfacesemiconductor-on-insulator (HSSOI) metal-oxide-semiconductor fieldeffect transistor (MOSFET) structure according to a first embodiment ofthe present invention.

FIGS. 8A-8F are various views of a variation of the first exemplaryHSSOI MOSFET structure according to the first embodiment of the presentinvention.

FIGS. 9A-13F are sequential views of a second exemplary hybrid surfacesemiconductor-on-insulator (HSSOI) metal-oxide-semiconductor fieldeffect transistor (MOSFET) structure according to a second embodiment ofthe present invention.

FIGS. 14A-14F are various views of a variation of the second exemplaryHSSOI MOSFET structure according to the second embodiment of the presentinvention.

FIGS. 15A-16F are sequential views of a third exemplary hybrid surfacesemiconductor-on-insulator (HSSOI) metal-oxide-semiconductor fieldeffect transistor (MOSFET) structure according to a third embodiment ofthe present invention.

FIGS. 17A-17F are various views of a variation of the third exemplaryHSSOI MOSFET structure according to the third embodiment of the presentinvention.

FIGS. 18A-18F are various views of a fourth exemplary HSSOI MOSFETstructure according to the fourth embodiment of the present invention.

FIGS. 19A-19F are various views of a fifth exemplary HSSOI MOSFETstructure according to the fifth embodiment of the present invention.

FIGS. 20A-20F are various views of a sixth exemplary HSSOI MOSFETstructure according to the sixth embodiment of the present invention.

DETAILED DESCRIPTION

As stated above, embodiments of the present invention relate to bodycontacted hybrid surface semiconductor-on-insulator (HSSOI) devicesformed on a semiconductor-on-insulator (SOI) substrate and methods ofmanufacturing the same, which are described herein with accompanyingfigures. Throughout the drawings, the same reference numerals or lettersare used to designate like or equivalent elements. The drawings are notnecessarily drawn to scale.

Referring to FIGS. 1A-1F, a first exemplary semiconductor structurecomprises a handle substrate 6, an insulator layer 10, a semiconductorfin 18, and a dielectric fin cap portion 30. The stack of the handlesubstrate 6, the insulator layer 10, and the semiconductor fin 18 may beformed by patterning a top semiconductor layer of asemiconductor-on-insulator (SOI) substrate. For example, an SOIcomprising the handle substrate 6, the insulator layer 10, and a topsemiconductor layer may be employed. In this case, the insulator layer10 is a buried insulator layer of the SOI substrate vertically abuttingthe handle substrate and the top semiconductor layer.

The handle substrate 6 may comprise a semiconductor material, aninsulator material, or a metallic material. For example, the handlesubstrate may comprise single crystalline semiconductor material such assilicon. The insulator layer 10 comprises a dielectric material such assilicon oxide or silicon nitride, or a semiconductor layer doped ordamaged to be substantially electrically insulating. The topsemiconductor layer comprises a semiconductor material. Preferably, thetop semiconductor material comprises a single crystalline semiconductormaterial having an epitaxial alignment among atoms within the entiretyof the top semiconductor layer. The semiconductor material may beselected from, but is not limited to, silicon, germanium,silicon-germanium alloy, silicon carbon alloy, silicon-germanium-carbonalloy, gallium arsenide, indium arsenide, indium phosphide, III-Vcompound semiconductor materials, II-VI compound semiconductormaterials, organic semiconductor materials, and other compoundsemiconductor materials. For example, the semiconductor material maycomprise single crystalline silicon. The thickness of the topsemiconductor layer may range from 1 nm to 2000 nm, or possibly 10 nm to200 nm, and typically from about 30 nm to about 120 nm, although lesserand greater thicknesses are also contemplated herein.

The semiconductor material within the top semiconductor layer may bedoped with electrical dopants of a first conductivity type. In the casewhere the first conductivity type is p-type, the electrical dopants maybe at least one of p-type dopants such as B, Ga, and In. In the casewhere the first conductivity type is n-type, the electrical dopants maybe at least one of n-type dopants such as P, As, and Sb. Typically, theconcentration of the electrical dopants may range from 1.0×10¹³atoms/cm³ to 1.0×10²⁰ atoms/cm³, or possibly 1.0×10¹⁴ atoms/cm³ to1.0×10¹⁹ atoms/cm³, although lesser and greater concentrations are alsocontemplated herein.

The top semiconductor layer may have a built-in stress in the planeperpendicular to the direction of the surface normal of an uppermostsurface of the top semiconductor layer. In addition or alternately, thetop semiconductor layer may have a built-in stress along the directionof the surface normal of the uppermost surface of the top semiconductorlayer. Embodiments of the present invention may be implemented in an SOIportion of a hybrid substrate that contains a bulk portion and the SOIportion. Such variations are explicitly contemplated herein.

The top surface of the semiconductor layer may be on a <100> orientedsilicon plane and the sidewalls on <110> silicon planes, with current inthe <110> direction. Alternatively the top surface may be a <110> planewith current in a <110> direction and the sidewalls on <100> typedirections.

A dielectric fin cap layer is formed on the top surface of the topsemiconductor layer. The dielectric fin cap layer comprises a dielectricmaterial such as a dielectric oxide, a dielectric nitride, or adielectric oxynitride. For example, the dielectric fin cap layercomprises silicon nitride or silicon oxide. The thickness of thedielectric fin cap layer may range from 0.5 nm to 1000 nm, or possibly 5nm to 100 nm, and typically from about 15 nm to about 50 nm, althoughlesser and greater thicknesses are also contemplated herein. Thedielectric fin cap layer may comprise a single homogeneous dielectricmaterial, or may comprise a vertical stack of at least two dielectricmaterial layers having different compositions.

The stack of the dielectric fin cap layer and the top semiconductorlayer is lithographically patterned to form a laterally isolatedstructure, which comprises a vertical stack of the semiconductor fin 18and the dielectric fin cap portion 30. Specifically, a remaining portionof the top semiconductor layer constitutes the semiconductor fin 18, anda remaining portion of the dielectric fin cap layer constitutes thedielectric fin cap portion 30.

The semiconductor fin 18 has a pair of substantially vertical sidewallswhich are parallel to each other. One of the pair of substantiallyvertical sidewalls is herein referred to as a “first sidewall,” and theother of the pair of substantially vertical sidewalls is herein referredto as a “second sidewall.” The semiconductor fin 18 may have anotherpair of substantially vertical sidewalls, wherein are herein referred toas a first end wall and a second end wall. Each of the first and secondend walls adjoins the first sidewall and the second sidewall. The firstsidewall, the second sidewall, the first end wall, and the second endwall of the semiconductor fin 18 are substantially vertically coincidentwith sidewalls of the dielectric fin cap portion 30. In all figures withthe suffix “B,” the first sidewall wall is located on a bottom side ofthe semiconductor fin 18 as represented in the two dimensional drawing,and the second sidewall is located on a top side of the semiconductorfin 18 as represented in the two dimensional drawing. In all figureswith the suffix “C,” the first end wall is located on the left side ofthe semiconductor fin 18 as represented in the two dimensional drawing,and the second end wall is located on the right side of thesemiconductor fin 18 as represented in the two dimensional drawing.

Referring to FIGS. 2A-2F, gate dielectrics 40 and a gate conductor 50are formed on the stack of the semiconductor fin 18 and the dielectricfin cap portion 30. While the bottom semiconductor layer 6 is omitted inFIGS. 2A-2F and in all subsequent drawings herein for conciseness, thepresence of the bottom semiconductor layer 6 directly underneath theinsulator layer 10 is presumed in all the figures hereafter.

The gate dielectrics 40 include a first gate dielectric located directlyon the first sidewall of the semiconductor fin 18 and a second gatedielectric located directly on the second sidewall of the semiconductorfin 18. The gate dielectrics 40 may comprise a semiconductor-baseddielectric material such as silicon oxide, silicon nitride, siliconoxynitride, and/or a stack thereof. The semiconductor-based dielectricmaterial may be formed by thermal conversion of exposed portions of thesemiconductor fin 18 and/or by chemical vapor deposition (CVD).Alternately, the gate dielectrics 40 may comprise a high-k dielectricmaterial such as HfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃,an alloy thereof, and a silicate thereof. The high-k dielectric materialmay be formed by methods well known in the art including, for example, achemical vapor deposition (CVD), an atomic layer deposition (ALD),molecular beam epitaxy (MBE), pulsed laser deposition (PLD), liquidsource misted chemical deposition (LSMCD), physical vapor deposition(PVD), etc. The thickness of the gate dielectric 40 may range from 0.1nm to 60 nm, or possibly 1 nm to 3 nm in the case of a conventionaldielectric material, and possibly 2 nm to 6 nm in the case of the high-kdielectric material, and may have an effective oxide thickness on theorder of or less than 1 nm to 10 nm.

The gate conductor 50 comprises a conductive material such as a dopedsemiconductor material, a conductive metallic nitride, a metallicmaterial, or a combination thereof. Exemplary doped semiconductormaterials include doped polysilicon, a doped silicon-containingsemiconductor alloy, etc. Exemplary conductive metallic nitridesinclude, but are not limited to, TaN, TiN, TiAlN, other conductiverefractory metal nitrides, or alloys thereof. Exemplary metallicmaterials include elemental metals and intermetallic alloys. Thethickness of the gate conductor 50, as measured above a top surface ofthe dielectric fin cap portion 30, may range from 2 nm to 4000 nm, orpossibly 20 nm to 400 nm, and typically from about 40 nm to about 200nm, although lesser and greater thicknesses are also contemplated hereinexplicitly. The thickness of the gate conductor 50 is greater than thethickness of the dielectric fin cap portion 30.

The gate dielectrics 40 and the gate conductor 50 may be formed byformation of a gate dielectric layer on the exposed surfaces of thesemiconductor fin 18, formation of a gate conductor layer directly onthe gate dielectric layer, and lithographic patterning of the stack ofthe gate conductor layer and the gate dielectric layer. The gatedielectric layer may be formed only on the surfaces of the semiconductorfin 18 and not on the surfaces of the dielectric fin cap portion 30,e.g., if the gate dielectric layer is formed by thermal or plasmaconversion of the semiconductor material of the semiconductor fin 18, ormay be formed on the surfaces of the semiconductor fin 18 and on the topsurface and sidewall surfaces of the dielectric fin cap portion 30,e.g., if the gate dielectric layer is formed by deposition of adielectric material.

The stack of the gate dielectric layer and the gate conductor arelithographically patterned so that the gate dielectrics 40, which is theremaining portion of the gate dielectric layer, and the gate conductor50, which is the remaining portion of the gate conductor layer, straddlea middle portion of the semiconductor fin 18 between a first end of thesemiconductor fin 18 and a second end of the semiconductor fin 18. Thus,a portion of the first sidewall, a portion of the second sidewall, andthe first end wall of the semiconductor fin 18 are exposed in the firstend of the semiconductor fin 18 located on one side of the dielectricfin cap portion 30, and another portion of the first sidewall, anotherportion of the second sidewall, and the second end wall of thesemiconductor fin 18 are exposed in the second end of the semiconductorfin 18 located on the other side of the dielectric fin cap portion 30.

The width of the gate dielectrics 40 and the gate conductor 50 along thehorizontal direction within the plane of the first and second sidewallsof the semiconductor fin 18 is the gate length of a hybrid surfacesemiconductor-on-insulator (HSSOI) metal-oxide-semiconductor fieldeffect transistor (MOSFET) to be formed in the first exemplarysemiconductor structure.

Optionally, halo ion implantation and/or source and drain extension ionimplantations may be performed at this step to form halo regions (notshown) and/or source and drain extension regions (not shown). A gatespacer 55 is formed on the sidewalls of the gate conductor 50 bydeposition of a conformal dielectric layer and an anisotropic etch. Aremaining portion of the conformal dielectric layer located on thesidewalls of the gate conductor 50 constitutes the gate spacer 55. Thegate spacer 55 may laterally surround the gate conductor 50. The gatespacer 55 abuts a top surface of the dielectric fin cap portion 30. Thegate spacer 55 may provide an offset between the edges of the gateconductor 50 and source and edges of the drain regions to besubsequently formed.

Depending on the ratio of the height of the exposed portion of thesidewall of the gate conductor 50 above the gate spacer 55 to the totalheight of the semiconductor fin 18 and the dielectric fin cap portion30, a residual dielectric spacer (not shown) may, or may not, be formedat the base of the first and second sidewalls and first and second endwalls of the semiconductor fin 18. Specifically, if the height of theexposed portion of the sidewall of the gate conductor 50 above the gatespacer 55 is greater than the total height of the semiconductor fin 18and the dielectric fin cap portion 30, no residual dielectric spacer isformed at the base of the semiconductor fin 18. If the height of theexposed portion of the sidewall of the gate conductor 50 above the gatespacer 55 is less than the total height of the semiconductor fin 18 andthe dielectric fin cap portion 30, residual dielectric spacers, whichare integrally formed with the gate spacer 55, are formed at the base ofthe semiconductor fin 18. The residual dielectric spacers and the gatespacer 55 abut the top surface of the insulator layer 10.

Referring to FIGS. 3A-3F, source and drain ion implantation is performedto implant dopants of a second conductivity type into the portion of thefirst sidewall in the first end, the portion of the second sidewall inthe first end, the portion of the first sidewall in the second end, theportion of the second sidewall in the second end, and the second endwall of the semiconductor fin 18. The second conductivity type is theopposite of the first conductivity type. For example, if the firstconductivity type is p-type, the second conductivity type is n-type, andvice versa. Angled ion implantation is employed to implant dopants ofthe second conductivity type through the first and second sidewalls andthe second end wall of the semiconductor fin 18. The directions ofangled ion implantation are shown schematically in FIGS. 3A and 3C. Thegate conductor 50 and the dielectric fin cap portion 30 function as amasking structure for the ion implantation.

The implantation depth of the dopants of the second conductivity type isselected to be less than one half of the width of the semiconductor fin18. The width of the semiconductor fin 18 is the distance between thefirst sidewall and the second sidewall of the semiconductor fin 18.First and second source regions 62 are formed directly beneath theportion of the first sidewall at the first end and directly beneath theportion of the second sidewall at the first end. The first and secondsource regions 62 are separated by a portion of the semiconductor fin 18having a doping of the first conductivity type that is not implantedwith dopants of the second conductivity type. Thus, the first sourceregion does not abut the second source region. The portion of thesemiconductor fin 18 having a doping of the first conductivity type isherein referred to as a body region 20, which functions as a body regionof the HSSOI MOSFET in embodiments of the present invention. Each of thefirst and second source regions 62 may have an edge that substantiallyvertically coincides with an edge of the gate conductor 50. Further,each of the first and second source regions 62 may abut a peripheralportion of the first and second gate dielectrics 40, respectively. Theoverlay between the first and second source regions 62 and the first andsecond gate dielectrics 40 may be adjusted with the thickness of thegate spacer 55 and/or with the tilt angles of the angled ionimplantation.

The drain region 64 extends from an edge of the first gate dielectricacross the portion of the first sidewall on the second end to the secondend wall, across the second end wall, across the second sidewall on thesecond end of the semiconductor fin 18, and to an edge of the secondgate dielectric. The drain region 64 is of integral and unitaryconstruction, i.e., connected together without a physically manifestedinterface and in a single contiguous piece. The drain region 64 includesa portion abutting the first sidewall, a second portion abutting thesecond end wall, and a third portion abutting the second sidewall. Theinterface between the drain region 64 and the body region 20 extendsfrom the bottom surface of the dielectric fin cap portion 30 to a topsurface of the insulator layer 10. The entirety of the interface betweenthe drain region 64 and the body region 20 may be substantiallyvertical. The drain region 64 functions as the drain of the HSSOI MOSFETin embodiments of the present invention. The drain region 64 may have anedge that substantially vertically coincides with an edge of the gateconductor 50. Further, the drain region 64 may abut a peripheral portionof each of the first and second gate dielectrics 40. The overlay betweenthe drain region 64 and the first and/or second gate dielectrics 40 maybe adjusted by employing a gate spacer and/or by adjusting tilt anglesof the angled ion implantation. The bottom surface of the dielectric fincap portion 30 vertically abuts the drain region 64 and the body region20.

Typically, the first and second source regions 62 and the drain region64 are heavily doped to provide low resistance in each of the first andsecond source regions 62 and the drain region 64. For example, thedopant concentration of the first and second source regions 62 and thedrain region 64 may range from 1.0×10¹⁸/cm³ to 1.0×10²²/cm³, or possibly1.0×10¹⁹/cm³ to 1.0×10²¹/cm³, although lesser and greater dopantconcentrations for the first and second source regions 62 and the drainregion 64 are also contemplated herein.

Referring to FIGS. 4A-4F, a photoresist 67 is applied over thesemiconductor fin 18 and the dielectric fin cap portion 30 and islithographically patterned to mask the second end of the semiconductorfin 18, while exposing the first end of the semiconductor fin 18. Anedge of the photoresist 67 may overlie the gate conductor 50.Alternately, an edge of the photoresist may overlie the gate spacer 55and completely cover the gate conductor 50. A sub-portion of thedielectric fin cap portion 30 located above the first end of thesemiconductor fin 18 is exposed. An anisotropic etch is employed toremove the sub-portion of the dielectric fin cap portion 30 that is notcovered by the gate conductor 50 or the photoresist 67. In the casewhere an edge of the photoresist 67 overlies the gate conductor 50, thegate conductor 50 and the photoresist 67 collectively function as anetch mask for the anisotropic etch. In the case where an edge of thephotoresist 67 overlies the gate spacer 55 and completely covers thegate conductor 50, the photoresist 67 is employed as an etch mask forthe anisotropic etch. An edge of the remaining portion of the dielectricfin cap portion 30 is substantially vertically coincident with the outeredge of the gate spacer 55 over the first end of the semiconductor fin18.

Preferably, the anisotropic etch is selective to the semiconductormaterial of the semiconductor fin 18. The anisotropic etch may, or maynot be selective to the insulator layer 10. Once the top surface of thefirst end of the semiconductor fin 18 is exposed, the photoresist 67 maybe removed. However, embodiments in which the removal of the photoresist67 is postponed until implantation of dopants of the first conductivitytype or until implantation of ions of a recombination-center-generatingelement, are also contemplated herein.

Referring to FIGS. 5A-5F, dopants of the first conductivity type may beimplanted into the exposed top surface of the first end of thesemiconductor fin 18. The top surface of the first end of thesemiconductor fin 18 prior to the ion implantation includes top surfacesof the first and second source regions 62 and a top surface of the bodyregion 20, which laterally abut the first and second source regions 62.The portion of the body region 20 which abuts the top surface of thefirst end of the semiconductor fin 18 and laterally abuts the first andsecond source regions 62 may be implanted with the dopants of the firstconductivity type to form a first-conductivity-type doped region whichis a modified semiconductor region 72. The thickness of the modifiedsemiconductor region 72 in this case where the modified semiconductorregion 72 is a first-conductivity-type doped region may range from 1 nmto 1000 nm, or possibly 10 nm to 100 nm, and typically from about 30 nmto about 60 nm, although lesser and greater thicknesses are alsocontemplated herein.

The dose of the ion implantation is set so that the implanted dopants ofthe first conductivity type do not change the type of doping of the topportions of the first and second source regions 62. In other words, thedopant concentration of dopants of the first conductivity type in themodified semiconductor region 72 is less than the dopant concentrationof dopants of the second conductivity type in the first and secondsource regions 62. For example, the dopant concentration of the modifiedsemiconductor region 72 may range from 1.0×10¹⁵/cm³ to 5.0×10²¹/cm³, orpossibly 1.0×10¹⁶/cm³ to 5.0×10²⁰/cm³, and typically from about1.0×10¹⁸/cm³ to about 1.0×10²⁰/cm³, although lesser and greater dopantconcentrations for the modified semiconductor region 72 are alsocontemplated herein. Due to the additional dopants of the firstconductivity type introduced into the modified semiconductor region 72,the modified semiconductor region 72 has a greater dopant concentrationthan the body region 20 in the semiconductor fin 18.

In one case, to form the modified semiconductor region 72 directlyunderneath the top surface of the first end of the semiconductor fin 18,the ion implantation of the dopants of the first conductivity type maybe performed without any tilt angle, i.e., in a direction normal to thetop surface of the semiconductor fin 18. The modified semiconductorregion 72 extends from an edge of the dielectric fin cap portion 30 onthe top surface of the semiconductor fin 18, across the top surface ofthe first end portion of the semiconductor fin 18 and to a horizontalline in the first end wall that is at the same level as the depth of themodified semiconductor region 72. In this case, the modifiedsemiconductor region 72 does not abut the insulator layer 10, and thefirst end wall comprises an exposed substantially vertical surface ofthe body region 20.

The gate conductor 50, the gate spacer 55, and the dielectric fin capportion 30 block the dopants of the first conductivity type during theimplantation to prevent introduction of the dopants of the firstconductivity type into the semiconductor fin 18. In the case where thephotoresist 67 is present at this step, the photoresist may also beemployed as an implantation mask. The photoresist 67, if present duringthe ion implantation, is removed subsequently.

In another case, the dopants of the first conductivity type may beimplanted into the first end wall by angled ion implantation. The tiltangle of the ion implantation is set so that dopants of the firstconductivity type are implanted through the first end wall, whileimplantation of dopants of the first conductivity type into the secondend wall is prevented. In this case, the modified semiconductor region72 extends from an edge of the dielectric fin cap portion 30 on the topsurface of the semiconductor fin 18, across the top surface of the firstend portion of the semiconductor fin 18, across the first end wall, andto the top surface of the insulator layer 10.

In yet another case, ions of a recombination-center-generating elementmay be implanted into the top surface of the first end of thesemiconductor fin 18 to form the modified semiconductor region 72. Thetop surface of the first end of the semiconductor fin 18 prior to theion implantation includes top surfaces of the first and second sourceregions 62 and a top surface of the body region 20, which laterally abutthe first and second source regions 62. The portion of the body region20 which abuts the top surface of the first end of the semiconductor fin18 and laterally abuts the first and second source regions 62 may beimplanted with the recombination-center-generating element to form arecombination-center-containing semiconductor region which is themodified semiconductor region 72.

Recombination-center-generating elements include, for example, nitrogen,oxygen, carbon, germanium, argon, krypton, xenon, gold, platinum, and acombination thereof. The recombination-center-generating elementimplanted into the modified semiconductor region 72 is not an electricaldopant belonging to group 3A or group 5A in the periodic table of theelements. Since the recombination-center-generating element isnon-electrical, no additional free hole or free electron is added to themodified semiconductor region 72.

The thickness of the modified semiconductor region 72 may range from 1nm to 1000 nm, or possibly 10 nm to 100 nm, and typically from about 30nm to about 60 nm, although lesser and greater thicknesses are alsocontemplated herein. The thickness of the modified semiconductor region72 is less than the thickness of the semiconductor fin 18. Theconcentration of the recombination-center-generating element may rangefrom 1.0×10¹¹/cm³ to 1.0×10²²/cm³, or possibly 1.0×10¹²/cm³ to1.0×10²¹/cm³, although lesser and greater concentrations are alsocontemplated herein. The dose of the recombination-center-generatingelement is determined to achieve the concentration range within thethickness of the modified semiconductor region 72.

The recombination-center-generating elements introduce damage to thecrystalline structure such as point defects and dislocations into themodified semiconductor region 72. Due to the presence of the implantedrecombination-center-generating elements, the modified semiconductorregion 72 maintains a high density of crystalline defects even afteractivation anneals that activate electrical dopants in the first andsecond source region 62 and the drain region 64. The high defect densityserves as a recombination center at which holes or electrons thataccumulate in the body region 20 are collected and annihilated byrecombination.

In one case, the modified semiconductor region 72 may have the sameconcentration of dopants of the first conductivity type as the bodyregion 20. No additional electrical dopants, i.e., dopants that providefree electrons or free holes such as group 3A elements and group 5Aelements, are added into the modified semiconductor region 72. Themodified semiconductor region 72 does not include dopants of the secondconductivity type.

In another case, dopants of the first conductivity type may be implantedinto the modified semiconductor region 72 by ion implantation. The doseof the ion implantation is set so that the implanted dopants of thefirst conductivity type do not change the type of doping of the topportions of the first and second source regions 62. In other words, thedopant concentration of dopants of the first conductivity type in themodified semiconductor region 72 is less than the dopant concentrationof dopants of the second conductivity type in the first and secondsource regions 62. For example, the concentration of dopants of thefirst conductivity type in the modified semiconductor region 72 mayrange from 1.0×10¹⁵/cm³ to 5.0×10²¹/cm³, or possibly 1.0×10¹⁶/cm³ to5.0×10²⁰/cm³, and typically from about 1.0×10¹⁸/cm³ to about1.0×10²⁰/cm³, although lesser and greater dopant concentrations for themodified semiconductor region 72 are also contemplated herein. Due tothe additional dopants of the first conductivity type that areintroduced into the modified semiconductor region 72, the modifiedsemiconductor region 72 has a greater dopant concentration than the bodyregion 20 in the semiconductor fin 18.

In one configuration, to form the modified semiconductor region 72directly underneath the top surface of the first end of thesemiconductor fin 18, the ion implantation of therecombination-center-generating element may be performed without anytilt angle, i.e., in a direction normal to the top surface of thesemiconductor fin 18. The modified semiconductor region 72 extends froman edge of the dielectric fin cap portion 30 on the top surface of thesemiconductor fin 18, across the top surface of the first end portion ofthe semiconductor fin 18 and to a horizontal line in the first end wallthat is at the same level as the depth of the modified semiconductorregion 72. In this case, the modified semiconductor region 72 does notabut the insulator layer 10, and the first end wall comprises an exposedsubstantially vertical surface of the body region 20.

The gate conductor 50, the gate spacer 55, and the dielectric fin capportion 30 block the recombination-center-generating element during theimplantation to prevent introduction of the ions of therecombination-center-generating element into the semiconductor fin 18.In the case where the photoresist 67 is present at this step, thephotoresist may also be employed as an implantation mask. Thephotoresist 67, if present during the ion implantation, is removedsubsequently.

In another configuration, the recombination-center-generating elementmay be implanted into the first end wall by angled ion implantation. Thetilt angle of the ion implantation is set so that the ions of therecombination-center-generating element are implanted through the firstend wall, while implantation of ions of therecombination-center-generating element into the second end wall isprevented. In this case, the modified semiconductor region 72 extendsfrom an edge of the dielectric fin cap portion 30 on the top surface ofthe semiconductor fin 18, across the top surface of the first endportion of the semiconductor fin 18, across the first end wall, and tothe top surface of the insulator layer 10.

Referring to FIGS. 6A-6F, metal semiconductor alloy portions are formedon exposed semiconductor surfaces of the semiconductor fin 18. The metalsemiconductor alloy portions may be formed, for example, by depositionof a metal layer on the exposed semiconductor surfaces and reaction ofthe metal layer with the semiconductor material underneath.

A source-side metal semiconductor alloy portion 82 is formed directly onthe outside surfaces of the first and second source regions 62, themodified semiconductor region 72, and any exposed surface of the bodyregion 20 on the first end wall, if present. Thus, source-side metalsemiconductor alloy portion 82 abuts, and is electrically shorted to,the first and second source regions 62, the modified semiconductorregion 72, and optionally, the body region 20 on the first end wall. Thesource-side metal semiconductor alloy portion 82 also abuts a sidewallsurface of the dielectric fin cap portion 30. The source-side metalsemiconductor alloy portion 82 may abut a top surface of the insulatorlayer 10 if residual dielectric spacers are not formed. The source-sidemetal semiconductor alloy portion 82 abuts residual dielectric spacersif residual dielectric spacers are present. The source-side metalsemiconductor alloy portion 82 is of integral and unitary construction.

A drain-side metal semiconductor alloy portion 84 is formed directly onthe outside surfaces of the drain region 64. The drain-side metalsemiconductor alloy portion 84 abuts the drain region 64, and does notabut the body region 20. The drain-side metal semiconductor alloyportion 84 also abuts a sidewall surface of the dielectric fin capportion 30. The drain-side metal semiconductor alloy portion 84 may abuta top surface of the insulator layer 10 if residual dielectric spacersare not formed. The drain-side metal semiconductor alloy portion 84abuts residual dielectric spacers if residual dielectric spacers arepresent. The drain-side metal semiconductor alloy portion 84 is ofintegral and unitary construction.

The source-side metal semiconductor alloy portion 82 and the drain-sidemetal semiconductor alloy portion 84 comprise an alloy of thesemiconductor material of the semiconductor fin 18 and the metal layer.In the case where the semiconductor fin 18 comprises silicon, thesource-side metal semiconductor alloy portion 82 and the drain-sidemetal semiconductor alloy portion 84 comprise a metal silicide. In thecase where the semiconductor fin 18 comprises a silicon-germanium alloy,the source-side metal semiconductor alloy portion 82 and the drain-sidemetal semiconductor alloy portion 84 may comprise a metalgermano-silicide. If the gate conductor 50 comprises a semiconductormaterial, a gate-side metal semiconductor alloy portion (not shown) maybe formed directly on the gate conductor 50.

Referring to FIGS. 7A-7F, a middle-of-line (MOL) dielectric layer 90 isformed over the semiconductor fin 18 and directly on the source-sidemetal semiconductor alloy portion 82, the drain-side metal semiconductoralloy portion 84, the dielectric fin cap portion 30, the gate spacer 55,and at least one of the gate conductor 50 or a gate-side metalsemiconductor alloy portion (not shown) formed directly on the gateconductor 50. The MOL dielectric layer 90 may comprise a silicon oxide,a silicon nitride, a chemical vapor deposition (CVD) low-k dielectricmaterial, a spin-on low-k dielectric material, or a stack thereof. TheMOL dielectric layer 90 may contain a mobile ion diffusion barrier layerthat prevents diffusion of mobile ions such as sodium and potassium fromback-end-of-line (BEOL) dielectric layers. Further, the MOL dielectriclayer 90 may contain a stress liner that applies tensile or compressivestress on underlying structures to alter charge carrier mobility in thechannels of the HSSOI MOSFET that are located directly beneath the firstand second gate dielectrics 40.

Contact via holes are formed in the MOL dielectric layer 90 and filledwith metal to form various metal contacts. For example, a source contactvia 92 vertically abutting the source-side metal semiconductor alloyportion 82 and at least one drain-side contact via 94 laterally abuttingthe drain-side metal semiconductor alloy portion 84 may be formed. Sincethe drain-side metal semiconductor alloy portion 84 is not formeddirectly on the top surface of the semiconductor fin 18, the at leastone drain-side contact via 94 laterally abuts the drain-side metalsemiconductor alloy portion 84. This may be accomplished by forming atleast one drain-side via hole that straddles the substantially verticalinterface between the drain region 64 and the drain-side metalsemiconductor alloy portion 84.

The HSSOI MOSFET may be oriented to take advantage of crystallographicorientations that may be selected from all possible orientations of thefirst and second sidewalls. Particularly, the surface orientation of thefirst and second sidewalls may be selected to maximize the chargecarrier mobility for the HSSOI MOSFET in the channels, which are locateddirectly beneath the first and second gate dielectrics 40. The bodyregion 20 of the HSSOI MOSFET is electrically connected to thesource-side metal semiconductor alloy portion 82 through the modifiedsemiconductor region 72.

Referring to FIGS. 8A-8F, a variation of the first exemplarysemiconductor structure may be derived from the first exemplarysemiconductor structure by implanting dopants of the second conductivitytype into the first end wall at the processing step corresponding toFIGS. 3A-3F. Angled ion implantation may be employed to implant dopantsof the second conductivity type into the first end wall, therebyconnecting the first and second source regions 62. An integrated sourceregion 62′ of integral and unitary construction is formed extending froman edge of the first gate dielectric across the portion of the firstsidewall on the first end to the first end wall, across the first endwall, across the second sidewall on the first end of the semiconductorfin 18, and to an edge of the second gate dielectric. The integratedsource region 62′ includes the first and second source regions 62 ofFIGS. 7A-7F.

Referring to FIGS. 9A-9F, a second exemplary semiconductor structureaccording to a second embodiment of the present invention is derivedfrom the first exemplary semiconductor structure of FIGS. 2A-2F. Aphotoresist 57 is applied over the semiconductor fin 18 and thedielectric fin cap portion 30 and is lithographically patterned to maskthe first end of the semiconductor fin 18, while exposing the second endof the semiconductor fin 18. An edge of the photoresist 57 may overliethe gate conductor 50. Alternately, an edge of the photoresist mayoverlie the gate spacer 55 and completely cover the gate conductor 50. Asub-portion of the dielectric fin cap portion 30 located above thesecond end of the semiconductor fin 18 is exposed. An anisotropic etchis employed to remove the sub-portion of the dielectric fin cap portion30 that is not covered by the gate conductor 50 or the photoresist 57.In the case where an edge of the photoresist 57 overlies the gateconductor 50, the gate conductor 50 and the photoresist 57 collectivelyfunction as an etch mask for the anisotropic etch. In the case where anedge of the photoresist 57 overlies the gate spacer 55 and completelycovers the gate conductor 50, the photoresist 57 is employed as an etchmask for the anisotropic etch. An edge of the remaining portion of thedielectric fin cap portion 30 is substantially vertically coincidentwith the outer edge of the gate spacer 55 over the second end of thesemiconductor fin 18.

Preferably, the anisotropic etch is selective to the semiconductormaterial of the semiconductor fin 18. The anisotropic etch may, or maynot be selective to the insulator layer 10. Once the top surface of thesecond end of the semiconductor fin 18 is exposed, the photoresist 57may be removed.

Referring to FIGS. 10A-10F, source and drain ion implantation isperformed to implant dopants of the second conductivity type into theportion of the first sidewall in the first end, the portion of thesecond sidewall in the first end, the portion of the first sidewall inthe second end, the portion of the second sidewall in the second end,and the second end wall of the semiconductor fin 18. As discussed above,the second conductivity type is the opposite of the first conductivitytype. Angled ion implantation is employed to implant dopants of thesecond conductivity type through the first and second sidewalls and thesecond end wall of the semiconductor fin 18. The directions of angledion implantation are shown schematically in FIGS. 10A and 10C. The gateconductor 50 and the dielectric fin cap portion 30 function as a maskingstructure for the ion implantation.

The implantation depth of the dopants of the second conductivity type isselected to be less than one half of the width of the semiconductor fin18, and, more typically, to a location slightly away from the finsidewalls. First and second source regions 62 are formed directlybeneath the portion of the first sidewall at the first end and directlybeneath the portion of the second sidewall at the first end in the samemanner as in the first embodiment.

The drain region 66 extends from an edge of the first gate dielectricacross the portion of the first sidewall on the second end to the secondend wall, across the second end wall, across the second sidewall on thesecond end of the semiconductor fin 18, and to an edge of the secondgate dielectric in the lateral direction. The drain region also extendsfrom the first sidewall on the second end, up to the top surface of thesecond end of the semiconductor fin 18, across the top surface of thesecond end of the semiconductor fin 18, and to the second sidewall onthe second end of the semiconductor fin 18. Thus, all exposed surfacesof the second end of the semiconductor fin are surfaces of the drainregion 66. The drain region 66 is of integral and unitary construction,i.e., connected together without a physically manifested interface andin a single contiguous piece.

The drain region 66 includes a portion abutting the first sidewall, asecond portion abutting the second end wall, a third portion abuttingthe second sidewall, and a fourth portion abutting the top surface ofthe second end of the semiconductor fin 18. The interface between thedrain region 66 and the body region 20 includes a substantiallyhorizontal surface between the fourth portion of the drain region 66 andthe body region 20 and substantially vertical surfaces between thefirst, second, and third portions of the drain region 20 and the bodyregion 20. Thus, a portion of the body region 20 underlies the drainregion 66. The drain region 66 functions as the drain of the HSSOIMOSFET in embodiments of the present invention. The drain region 66 mayhave an edge that substantially vertically coincides with an edge of thegate conductor 50. Further, the drain region 66 may abut a peripheralportion of each of the first and second gate dielectric 40. The overlaybetween the drain region 66 and the first and/or second gate dielectrics40 may be adjusted with the thickness of the gate spacer 55 and/or withthe tilt angles of the angled ion implantation. The bottom surface ofthe dielectric fin cap portion 30 vertically abuts the drain region 66and the body region 20.

Typically, the first and second source regions 62 and the drain region66 are heavily doped to provide low resistance in each of the first andsecond source regions 62 and the drain region 66. For example, thedopant concentration of the first and second source regions 62 and thedrain region 66 may range from 1.0×10¹⁸/cm³ to 1.0×10²²/cm³, or possibly1.0×10¹⁹/cm³ to 1.0×10²¹/cm³, although lesser and greater dopantconcentrations for the first and second source regions 62 and the drainregion 66 are also contemplated herein.

Referring to FIGS. 11A-11F, the exposed sub-portion of the dielectricfin cap portion 30 over the first end of the semiconductor fin 18 andnot covered by the gate conductor 50 or the gate spacer 55 is removed byan etch, which may be an anisotropic ion etch or an isotropic etch. Thegate conductor 50 and the gate spacer 55 are collectively employed as anetch mask. Preferably, the etch is selective to the material of thesemiconductor fin 18. Not necessarily but preferably, the etch isselective to the material of the insulator layer 10. The top surface ofthe first end of the semiconductor fin 18 is exposed after the etch.

Dopants of the first conductivity type are implanted into the exposedtop surfaces of the first end and the second end of the semiconductorfin 18. The top surface of the first end of the semiconductor fin 18prior to the ion implantation includes top surfaces of the first andsecond source regions 62 and a top surface of the body region 20, whichlaterally abut the first and second source regions 62. The top surfaceof the second end of the semiconductor fin 18 prior to the ionimplantation is a top surface of the drain region 66.

The portion of the body region 20 which abuts the top surface of thefirst end of the semiconductor fin 18 and laterally abuts the first andsecond source regions 62 is implanted with the dopants of the firstconductivity type to form a modified semiconductor region 72. Thethickness of the modified semiconductor region 72 may range from 1 nm to1000 nm, or possibly 10 nm to 100 nm, and typically from about 30 nm toabout 60 nm, although lesser and greater thicknesses are alsocontemplated herein.

The dose of the ion implantation is set so that the implanted dopants ofthe first conductivity type do not change the type of doping of the topportions of the first and second source regions 62 Likewise, theimplanted dopants of the first conductivity type do not change the typeof doping of the implanted top portion of the drain region 66. Thedopant concentration of dopants of the first conductivity type in themodified semiconductor region 72 is less than the dopant concentrationof dopants of the second conductivity type in the first and secondsource regions 62 and in the drain region 66. For example, the dopantconcentration of the modified semiconductor region 72 may range from1.0×10¹⁵/cm³ to 5.0×10²¹/cm³, or possibly 1.0×10¹⁶/cm³ to 5.0×10²⁰/cm³,and typically from about 1.0×10¹⁸/cm³ to about 1.0×10²⁰/cm³, althoughlesser and greater dopant concentrations for the modified semiconductorregion 72 are also contemplated herein. Due to the additional dopants ofthe first conductivity type introduced into the modified semiconductorregion 72, the modified semiconductor region 72 has a greater dopantconcentration than the body region 20 in the semiconductor fin 18.

In one case, to form the modified semiconductor region 72 directlyunderneath the top surface of the first end of the semiconductor fin 18,the ion implantation of the dopants of the first conductivity type maybe performed without any tilt angle, i.e., in a direction normal to thetop surface of the semiconductor fin 18. The modified semiconductorregion 72 extends from an edge of the dielectric fin cap portion 30 onthe top surface of the semiconductor fin 18, across the top surface ofthe first end portion of the semiconductor fin 18 and to a horizontalline in the first end wall that is at the same level as the depth of themodified semiconductor region 72. In this case, the modifiedsemiconductor region 72 does not abut the insulator layer 10, and thefirst end wall comprises an exposed substantially vertical surface ofthe body region 20.

The gate conductor 50, the gate spacer 55, and the dielectric fin capportion 30 block the dopants of the first conductivity type during theimplantation to prevent introduction of the dopants of the firstconductivity type into the semiconductor fin 18.

In another case, the dopants of the first conductivity type may beimplanted into the first end wall by angled ion implantation. The tiltangle of the ion implantation is set so that dopants of the firstconductivity type are implanted through the first end wall, whileimplantation of dopants of the first conductivity type into the secondend wall is prevented. In this case, the modified semiconductor region72 extends from an edge of the dielectric fin cap portion 30 on the topsurface of the semiconductor fin 18, across the top surface of the firstend portion of the semiconductor fin 18, across the first end wall, andto the top surface of the insulator layer 10.

In yet another case, ions of the recombination-center-generating elementmay be implanted into the exposed top surfaces of the first end and thesecond end of the semiconductor fin 18 in the same manner as in thefirst embodiment. The top surface of the first end of the semiconductorfin 18 prior to the ion implantation includes top surfaces of the firstand second source regions 62 and a top surface of the body region 20,which laterally abut the first and second source regions 62. The topsurface of the second end of the semiconductor fin 18 prior to the ionimplantation is a top surface of the drain region 66.

The portion of the body region 20 which abuts the top surface of thefirst end of the semiconductor fin 18 and laterally abuts the first andsecond source regions 62 may be implanted with the ions of therecombination-center-generating element to form a modified semiconductorregion 72. The thickness of the modified semiconductor region 72 mayrange from 1 nm to 1000 nm, or possibly 10 nm to 100 nm, and typicallyfrom about 30 nm to about 60 nm, although lesser and greater thicknessesare also contemplated herein. The atomic concentration of therecombination-center-generating element may be the same as in the firstembodiment.

The modified semiconductor region 72 may have the same atomicconcentration of dopants of the first conductivity as the body region20, or may have a higher atomic concentration of dopants of the firstconductivity type than the body region 20. In the case where anyadditional dopants of the first conductivity are introduced into themodified semiconductor region 72, the same methods may be employed as inthe first embodiment.

In one case, to form the modified semiconductor region 72 directlyunderneath the top surface of the first end of the semiconductor fin 18,the ion implantation of the recombination-center-generating element maybe performed without any tilt angle, i.e., in a direction normal to thetop surface of the semiconductor fin 18. The modified semiconductorregion 72 extends from an edge of the dielectric fin cap portion 30 onthe top surface of the semiconductor fin 18, across the top surface ofthe first end portion of the semiconductor fin 18 and to a horizontalline in the first end wall that is at the same level as the depth of themodified semiconductor region 72. In this case, the modifiedsemiconductor region 72 does not abut the insulator layer 10, and thefirst end wall comprises an exposed substantially vertical surface ofthe body region 20.

The gate conductor 50, the gate spacer 55, and the dielectric fin capportion 30 block the ions of the recombination-center-generating elementduring the implantation to prevent introduction of therecombination-center-generating element into the semiconductor fin 18.

In another case, the ions of the recombination-center-generating elementmay be implanted into the first end wall by angled ion implantation. Thetilt angle of the ion implantation is set so that ions of therecombination-center-generating element are implanted through the firstend wall, while implantation of ions of therecombination-center-generating element into the second end wall may beprevented. In this case, the modified semiconductor region 72 extendsfrom an edge of the dielectric fin cap portion 30 on the top surface ofthe semiconductor fin 18, across the top surface of the first endportion of the semiconductor fin 18, across the first end wall, and tothe top surface of the insulator layer 10.

Referring to FIGS. 12A-12F, metal semiconductor alloy portions areformed on exposed semiconductor surfaces of the semiconductor fin 18 inthe same manner as in the first embodiment. A source-side metalsemiconductor alloy portion 82 is formed directly on the outsidesurfaces of the first and second source regions 62, the modifiedsemiconductor region 72, and any exposed surface of the body region 20on the first end wall, if present. The source-side metal semiconductoralloy portion 82 may abut a top surface of the insulator layer 10 ifresidual dielectric spacers are not formed. The source-side metalsemiconductor alloy portion 82 abuts residual dielectric spacers ifresidual dielectric spacers are present. The source-side metalsemiconductor alloy portion 82 is of integral and unitary construction.

A drain-side metal semiconductor alloy portion 86 is formed directly onthe outside surfaces of the drain region 66. Specifically, thedrain-side metal semiconductor alloy portion is formed directly on thesecond end of the first sidewall, the second end of the second sidewall,the second end wall, and the top surface of the second end of thesemiconductor fin 18. Thus, a sub-portion of the drain-side metalsemiconductor alloy portion 86 overlies the drain region 66 and aportion of the body region 20. The drain-side metal semiconductor alloyportion 86 abuts the drain region 66, and does not abut the body region20. The drain-side metal semiconductor alloy portion 86 also abuts asidewall surface of the dielectric fin cap portion 30, in which thesidewall surface is substantially vertically coincident with an edge ofthe gate spacer 55. The drain-side metal semiconductor alloy portion 86may abut a top surface of the insulator layer 10 if residual dielectricspacers are not formed. The drain-side metal semiconductor alloy portion86 abuts residual dielectric spacers if residual dielectric spacers arepresent. The drain-side metal semiconductor alloy portion 86 is ofintegral and unitary construction.

The source-side metal semiconductor alloy portion 82 and the drain-sidemetal semiconductor alloy portion 86 comprise an alloy of thesemiconductor material of the semiconductor fin 18 and the metal layeras in the first embodiment.

Referring to FIGS. 13A-13F, a middle-of-line (MOL) dielectric layer 90is formed over the semiconductor fin 18 as in the first embodiment.Contact via holes are formed in the MOL dielectric layer 90 and filledwith metal to form various metal contacts. For example, a source contactvia 92 vertically abutting the source-side metal semiconductor alloyportion 82 and a drain-side contact via 94 vertically abutting thedrain-side metal semiconductor alloy portion 86 may be formed. Since thedrain-side metal semiconductor alloy portion 86 is formed directly onthe top surface of the semiconductor fin 18, the drain-side contact viavertically abuts the drain-side metal semiconductor alloy portion 86.

The HSSOI MOSFET may be oriented to take advantage of crystallographicorientations that may be selected from all possible orientations of thefirst and second sidewalls as in the first embodiment. The body region20 of the HSSOI MOSFET is electrically connected to the source-sidemetal semiconductor alloy portion 82 through the modified semiconductorregion 72.

Referring to FIGS. 14A-14F, a variation of the second exemplarysemiconductor structure may be derived from the second exemplarysemiconductor structure by implanting dopants of the second conductivitytype into the first end wall at the processing step corresponding toFIGS. 11A-11F. Angled ion implantation may be employed to implantdopants of the second conductivity type into the first end wall, therebyconnecting the first and second source regions 62. An integrated sourceregion 62′ of integral and unitary construction is formed extending froman edge of the first gate dielectric across the portion of the firstsidewall on the first end to the first end wall, across the first endwall, across the second sidewall on the first end of the semiconductorfin 18, and to an edge of the second gate dielectric. The integratedsource region 62′ includes the first and second source regions 62 ofFIGS. 13A-13F.

Referring to FIGS. 15A-15F, a third exemplary semiconductor structureaccording to a third embodiment of the present invention is derived fromthe second exemplary semiconductor structure of FIGS. 10A-10F. Angledion implantation is employed to implant dopants of the secondconductivity type through the first and second sidewalls and the secondend wall of the semiconductor fin 18 as in the second embodiment. Duringthe source and drain ion implantation, however, the energy and dose ofdopants of the second conductivity type that are implanted into thesecond end of the semiconductor fin 18 are adjusted so that the entiretyof the second end of the semiconductor fin 18 has a doping of the secondconductivity type. In other words, the entirety of the second end of thesemiconductor fin 18 becomes a drain region 68. The drain region 68 isof integral and unitary construction, i.e., connected together without aphysically manifested interface and in a single contiguous piece.

The entirety of the interface between the drain region 68 and the bodyregion 20 is substantially vertical. The interface between the drainregion 68 and the body region 20 extends from a bottom surface of thedielectric fin cap portion 30 to a top surface of the insulator layer10. The drain region 68 does not overlie the body region 20, andvertically abuts the insulator layer 10. The directions of angled ionimplantation are shown schematically in FIGS. 15A and 15C. The gateconductor 50 and the dielectric fin cap portion 30 function as a maskingstructure for the ion implantation. The first and second source regions62 of the third embodiment may be identical to the first and secondsource regions 62 of the second embodiment.

The drain region 68 functions as the drain of the HSSOI MOSFET inembodiments of the present invention. The drain region 68 may have anedge that substantially vertically coincides with an edge of the gateconductor 50. Further, the drain region 68 may abut a peripheral portionof each of the first and second gate dielectric 40. The overlay betweenthe drain region 68 and the first and/or second gate dielectrics 40 maybe adjusted with the thickness of the gate spacer 55 and/or with thetilt angles of the angled ion implantation. The bottom surface of thedielectric fin cap portion 30 vertically abuts the drain region 68 andthe body region 20.

Typically, the first and second source regions 62 and the drain region68 are heavily doped to provide low resistance in each of the first andsecond source regions 62 and the drain region 68. For example, thedopant concentration of the first and second source regions 62 and thedrain region 68 may range from 1.0×10¹⁸/cm³ to 1.0×10²²/cm³, or possibly1.0×10¹⁹/cm³ to 1.0×10²¹/cm³, although lesser and greater dopantconcentrations for the first and second source regions 62 and the drainregion 68 are also contemplated herein.

Referring to FIGS. 16A-16F, processing steps corresponding to FIGS.11A-13F are performed as in the second embodiment. As in the first andsecond embodiments, the HSSOI MOSFET may be oriented to take advantageof crystallographic orientations that may be selected from all possibleorientations of the first and second sidewalls. The body region 20 ofthe HSSOI MOSFET is electrically connected to the source-side metalsemiconductor alloy portion 82 through the modified semiconductor region72.

Referring to FIGS. 17A-17F, a variation of the third exemplarysemiconductor structure may be derived from the third exemplarysemiconductor structure by implanting dopants of the second conductivitytype into the first end wall at the processing step corresponding toFIGS. 11A-11F. Angled ion implantation may be employed to implantdopants of the second conductivity type into the first end wall, therebyconnecting the first and second source regions 62. An integrated sourceregion 62′ of integral and unitary construction is formed extending froman edge of the first gate dielectric across the portion of the firstsidewall on the first end to the first end wall, across the first endwall, across the second sidewall on the first end of the semiconductorfin 18, and to an edge of the second gate dielectric. The integratedsource region 62′ includes the first and second source regions 62 ofFIGS. 16A-16F.

Referring to FIGS. 18A-18F, a fourth exemplary semiconductor structureaccording to a fourth embodiment of the present invention is derivedfrom the first exemplary semiconductor structure by omitting theformation of the modified semiconductor region 72 at the processing stepcorresponding to FIGS. 5A-5F. Thus, the source-side metal semiconductoralloy portion 82 abuts the first and second source regions 62 and theportion of the body region 20 located between the first and secondsource regions 62. As in the previous embodiments, the HSSOI MOSFET maybe oriented to take advantage of crystallographic orientations that maybe selected from all possible orientations of the first and secondsidewalls. The body region 20 of the HSSOI MOSFET is electricallyconnected to the source-side metal semiconductor alloy portion 82directly.

Referring to FIGS. 19A-19F, a fifth exemplary semiconductor structureaccording to a fifth embodiment of the present invention is derived fromthe second exemplary semiconductor structure by omitting the formationof the modified semiconductor region 72 at the processing stepcorresponding to FIGS. 11A-11F. Thus, the source-side metalsemiconductor alloy portion 82 abuts the first and second source regions62 and the portion of the body region 20 located between the first andsecond source regions 62. As in the previous embodiments, the HSSOIMOSFET may be oriented to take advantage of crystallographicorientations that may be selected from all possible orientations of thefirst and second sidewalls. The body region 20 of the HSSOI MOSFET iselectrically connected to the source-side metal semiconductor alloyportion 82 directly.

Referring to FIGS. 20A-20F, a sixth exemplary semiconductor structureaccording to a sixth embodiment of the present invention is derived fromthe third exemplary semiconductor structure by omitting the formation ofthe modified semiconductor region 72 at the processing stepcorresponding to FIGS. 11A-11F. Thus, the source-side metalsemiconductor alloy portion 82 abuts the first and second source regions62 and the portion of the body region 20 located between the first andsecond source regions 62. As in the previous embodiments, the HSSOIMOSFET may be oriented to take advantage of crystallographicorientations that may be selected from all possible orientations of thefirst and second sidewalls. The body region 20 of the HSSOI MOSFET iselectrically connected to the source-side metal semiconductor alloyportion 82 directly.

While the invention has been described in terms of specific embodiments,it is evident in view of the foregoing description that numerousalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the invention is intended to encompassall such alternatives, modifications and variations which fall withinthe scope and spirit of the invention and the following claims.

What is claimed is:
 1. A method of forming a semiconductor structurecomprising: forming a semiconductor fin having a first sidewall, asecond sidewall, and a substantially horizontal top surface and locateddirectly on an insulator layer and having a doping of a firstconductivity type, wherein said first and second sidewalls aresubstantially parallel to each other and substantially vertical; forminga recombination-center-containing semiconductor region directlyunderneath said substantially horizontal top surface and including asemiconductor material and having a doping of said first conductivitytype; and forming a metal semiconductor alloy portion directly on saidrecombination-center-containing semiconductor region and at least onesource region formed within said semiconductor fin and having a dopingof a second conductivity type, wherein said second conductivity type isthe opposite of said first conductivity type.
 2. The method of claim 1,wherein said recombination-center-containing semiconductor regioncomprises recombination-center-generating elements that do not add anyadditional free hole or any additional free electron
 3. The method ofclaim 2, wherein said recombination-center-generating elements areselected from nitrogen, oxygen, carbon, germanium, argon, krypton,xenon, gold, platinum, and a combination thereof.
 3. The method of claim2, wherein a concentration of said recombination-center-generatingelements is in a range from 1.0×10¹¹/cm³ to 1.0×10²²/cm³.
 4. The methodof claim 2, wherein a thickness of said recombination-center-generatingsemiconductor region is less than a thickness of said semiconductor fin.5. The method of claim 1, wherein said recombination-center-containingsemiconductor region is formed by ion implantation ofrecombination-center-generating elements.
 6. The method of claim 5,wherein said recombination-center-generating elements introduce damageto a crystalline structure such as point defects and dislocations
 7. Themethod of claim 5, wherein said recombination-center-generating elementsare implanted into a first end wall of said semiconductor fin by angledion implantation.
 8. The method of claim 7, wherein a tilt angle of saidion implantation is set so that ions of saidrecombination-center-generating elements are implanted through saidfirst end wall, while implantation of ions of saidrecombination-center-generating elements into a second end wall of saidsemiconductor fin is prevented.
 9. The method of claim 5, wherein saidimplantation of said recombination-center-generating element isperformed without any tilt angle in a direction normal to saidsubstantially horizontal top surface of said semiconductor fin
 10. Themethod of claim 1, further comprising: forming a first source regionhaving a doping of a second conductivity type directly on said firstsidewall within a first end of said semiconductor fin, wherein saidsecond conductivity type is the opposite of said first conductivitytype; forming a second source region having a doping of said secondconductivity type directly on said second sidewall within said first endof said semiconductor fin.
 11. The method of claim 10, furthercomprising forming a drain region within a second end of saidsemiconductor fin and having a doping of said second conductivity type,wherein said drain region does not abut said first and second sourceregions, and wherein said second end is located at an opposite side ofsaid first end.
 12. The method of claim 11, wherein said first sourceregion, said second source region, and said drain region are formed byimplantation of ions of said second conductivity type.
 13. The method ofclaim 11, wherein said drain region is contiguous and includes a portionlocated directly on an end wall of said semiconductor fin, wherein saidend wall is substantially perpendicular to said first sidewall and saidsecond sidewall and is directly adjoined to said first sidewall and saidsecond sidewall.
 14. The method of claim 11, further comprising:providing a semiconductor-on-insulator (SOI) layer including saidinsulator layer and a top semiconductor layer; and forming a dielectricfin cap layer on said top semiconductor layer.
 15. The method of claim14, further comprising patterning said dielectric fin cap layer and saidtop semiconductor layer, wherein a remaining portion of said dielectricfin cap layer constitutes a dielectric fin cap portion, wherein aremaining portion of said top semiconductor layer constitutes saidsemiconductor fin, and wherein said first sidewall and said secondsidewall are substantially vertically coincident with sidewalls of saiddielectric fin cap portion.
 16. The method of claim 15, wherein saiddielectric fin cap portion overlies an entirety of said drain region,and wherein an edge of said dielectric fin cap portion is substantiallyaligned to said gate conductor.
 17. The method of claim 15, furthercomprising implanting dopants of said first conductivity type through aportion of said substantially horizontal top surface of saidsemiconductor fin located between said first source region and saidsecond source region to form a first-conductivity-type doped region. 18.The method of claim 14, further comprising: forming a first gatedielectric directly on a middle portion of said first sidewall; forminga second gate dielectric directly on a middle portion of said secondsidewall; and forming a gate conductor directly on said first gatedielectric, said second gate dielectric, and said dielectric fin capportion.
 19. The method of claim 1, wherein said metal semiconductoralloy portion is formed as a structure that contiguously extends from asurface of said first source region to a surface of said second sourceregion, and to said top surface of said portion of said semiconductorfin.
 20. The method of claim 1, further comprising forming a stack of abody region and a semiconductor region within said semiconductor fin,wherein an interface between said body region and said semiconductorregion extends to a first end wall.